This invention relates to improvements in a rake for removing refuse and debris accumulated against a screen disposed in a flowing waterstream of sewage, industrial waste and the like on its way to a treatment plant.
The handling and treatment of sewage and other waste materials is a continuing problem wherever population centers exist in order to meet the objectives of safe sanitary requirements. Sewer flows abound with an infinite variety of extraneous objects such as logs, sticks, rags, plastic items, rubber, stone, metal and the like which must be removed or reduced in size before the sewer waterstream reaches the treatment facilities and well known devices for such purposes include bar racks or screens, coarse screens and rotary disc and drum screens to intercept material together with comminutors that reduce materials to small dimensions.
Typically, the removal device is in the line of flow to intercept the debris and such removal devices usually have various mechanical rake means for collecting the debris accumulations since manual removable by grab hooks and the like is generally unsatisfactory. The collected debris in some systems is passed through a comminutor for return to the waterstream and in other systems, it is buried or otherwise disposed of with sanitary engineers having opinions both pro and con as to the advantages and disadvantages of each system.
The present invention is concerned with improvements for the operation of the mechanical rake relative to a screen device of the type indicated and for the purpose of illustrating this invention, I have preferably shown it on the well known bar screen type of debris removal device which is formed by a plurality of spaced parallel longitudinal bar grates disposed on an inclined plane in a flowing stream of sewage and it will be understood that such invention may also be used with other screening devices having mechanical rakes. This invention, as will appear, is also shown for illustration in use in combination with a communitor for grinding the collected debris and returning it to the waterstream but such comminutor forms no part of this invention and is not required as a part thereof as the accumulations on the screen can be delivered to any desired point for disposition or treatment other than as illustrated herein.
In the use of a bar screen as noted above, the accompanying mechanical rake, to be effective, must operate in the cycle of an operational debris engaging stroke and a non-debris engaging return stroke and various devices for such purposes are exemplified in U.S. Pat. nos. 2,128,345, 2,904,181, 3,358,837 and 4,138,334 where the mechanisms shown appear to be sophisticated in nature and where the location of parts extending over a relatively wide area between distant ends of the overall cleaning structure and sometimes into the waterstream increases the difficulty of accessibility to the various working parts for servicing and maintenance.
Accordingly, in view of the above observations and as a result of many years of experience in the operation of sewage disposal systems, it is one of the important objects of this invention to provide improved operating means for a rake on a bar screen in a sewage system that is simple in construction, highly effective and efficient in operation, economical to manufacture and designed to operate with a minimum of servicing and maintenance over long periods of time without breakdown or stoppage.
Another object herein is to provide a rake of the above class wherein the operation and non-operational strokes are effected by an endless chain drive assembly for which all components thereof are compactly arranged at a point remote from the debris intercepting end of the bar screen structure so that said assembly is free of contact with the waterstream and conveniently accessible for servicing and maintenance.
A further object herein is to provide a rake as characterized that operates at the debris intercepting end of the screen structure by connection through elongated rod members to a remotely disposed chain drive assembly that moves the rake in its cleaning stroke on a lower track in engagement with the screen and at the end of such stroke, elevates the rake into registration with an upper track and moves it thereon out of engagement with the screen in a return stroke to a point where the rake drops by gravity to the lower track in position for another cleaning stroke.
Still another object is to provide a bar screen rake movable by a chain drive assembly as characterized where, in the movement of the rake from its cleaning stroke to its return stroke, it is tilted by such assembly to a degree permitting any accumulations thereon to fall by gravity for a self-cleaning capability.
The foregoing objects and such further objects as may appear herein, or be hereinafter pointed out, together with the advantages of this invention will be more fully discussed and developed in the more detailed description of the accompanying drawings.